Fahrenheit to Celsius conversion yields only 0.0 and -0.0

Question

I'm on the 8th chapter (Methods, Constructors, and Fields) of my Java methods book and I'm having a problem with one of my exercises.

The provided code is Temperature.java

  import java.awt.*;
  import java.awt.event.*;
  import javax.swing.*;
  import java.text.DecimalFormat;

  public class Temperature extends JApplet
   implements ActionListener {
      private JTextField displayF, displayC;
      private static DecimalFormat displayFormat = new DecimalFormat("0.0");

      public void init() {
          Container c = getContentPane();
          c.setBackground(Color.white);
          c.setLayout(new GridLayout(2, 2, 10, 0));

          c.add(new JLabel("  Fahrenheit:"));
          c.add(new JLabel("  Celsius:"));

          displayF = new JTextField(6);
          displayF.setBackground(Color.yellow);
          displayF.addActionListener(this);
          c.add(displayF);

          displayC = new JTextField(6);
          displayC.setBackground(Color.yellow);
          displayC.addActionListener(this);
          c.add(displayC);
      }

      public void actionPerformed(ActionEvent e) {
          String s;
          double degrees;
          FCConverter fc = new FCConverter();

          if ((JTextField) e.getSource() == displayF) {
              s = displayF.getText().trim();
              degrees = Double.parseDouble(s);
              fc.setFahrenheit(degrees);
              degrees = fc.getCelsius();
              displayC.setText(displayFormat.format(degrees));
          } else {
              s = displayC.getText().trim();
              degrees = Double.parseDouble(s);
              fc.setCelsius(degrees);
              degrees = fc.getFahrenheit();
              displayF.setText(displayFormat.format(degrees));
          }
      }
  }

And from there I'm supposed to write and test FCConverter.java I've come up with:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.text.DecimalFormat;

public class FCConverter
{
  private double Celsius;
  private double Fahrenheit;
  public double setFahrenheit (double degrees)
  {
      Celsius = (degrees - 32) * (5 / 9);
      return 0;
  }
  public double getCelsius ()
  {
      return Celsius;
  }
  public double setCelsius (double degrees)
  {
  Fahrenheit = (degrees * 9 / 5 + 32);
          return 0;
  }
  public double getFahrenheit ()
  {
      return Fahrenheit;
  }
}

It's probably horrendous in terms of style, but I just wanted to get some working code that got past the compiler (hence the "return 0;"s which I'm fairly certain can be circumvented in a much more fashionable manner).

What I want to know is, when I test this in appletviewer or in browser form, the Celsius to Fahrenheit conversion works fine, but the Fahrenheit to Celsius conversion yields only 0.0 and -0.0. I don't understand what's wrong since the part I've designed seems fairly symmetrical. Shouldn't it be the case that both or neither conversion method works?

Answer 1

In integer math (5 / 9) = 0.

and (degrees - 32) * (5 / 9); will always be 0 you need to use doubles or something.

Answer 2

The problem seems to be 5/9. They are seen as an integer, and 5/9 is 0.something which is 0 as an integer. So whatever * 0 = +-0 :)

Place a "d" after the numbers, (5d/9d) forcing the compiler to consider them doubles.

Answer 3

change (5 / 9) to (5.0 / 9.0) to let java know, that you want real numbers division.

Answer 4

If you don't return anything set the return type to void. If you like to return doubles, you have to use doubles in calculations. 5/9 is always zero because 5 and 9 are integers. 5.0/9.0 is a different calculation on doubles.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.text.DecimalFormat;

public class FCConverter
{
  private double Celsius;
  private double Fahrenheit;
  public void setFahrenheit (double degrees)
  {
     Celsius = (degrees - 32.0) * (5.0 / 9.0);
  }
  public double getCelsius ()
  {
      return Celsius;
  }
  public void setCelsius (double degrees)
  {
      Fahrenheit = (degrees * 9.0 / 5.0 + 32.0);
  }
  public double getFahrenheit ()
  {
      return Fahrenheit;
  }
}

Answer 5

import java.util.Scanner;
public class HelloWorld {

    public static void main(String[] args) {
        Scanner reader = new Scanner(System.in);  // Reading from System.in

        System.out.println("Enter  the number of Fahrenheit temperatures to convert to Kelvins");
// opts for the user to enter a number 

        int F = reader.nextInt() ; // Scans the next token of the input
        double f = 5/9d;
        System.out.println(f);
        double x = F -32;
        System.out.println(x);
        double K = (f*x)+ 273.0; // the formulae to calculate temperature  in Kelvin
        System.out.println( +F + " Fahrenheit is equal " +K + " Kelvins" ) ;
        reader.close();




    }       

}